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presentationanatomyslides

presentationanatomyslides - Lymph node Lymphnodes ....

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Lymph node
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Lymph nodes Lymph nodes are small bean shaped structures lying along the course of lymphatics. They are aggregated in particular sites  such as the neck, axillae, groins and para-aortic region. Knowledge of the sites of lymph nodes is important in physical  examination of patients. Lymph nodes have two main functions: •phagocytic cells act as filters for particulate matter and micro-organisms •antigen is presented to the immune system a) Structure Lymph nodes have a fibrous capsule from which trabeculae extend towards the centre thus forming a framework: The node is made up of three components: •lymphatic sinuses •blood vessels parenchyma (cortex, paracortex, medulla)  b) Cortex B cells:  These enter the lymph node via HEVs and pass to the follicles. If activated by antigenic stimulation they proliferate  and remain in the node. Unstimulated B cells, however, pass out rapidly from the node to return to the general circulation.  Activated B cells within the lymphoid follicles are known as follicle centre cells. The pale staining central area of a secondary  follicle is known as a germinal centre and this is surrounded by a mantle zone consisting of small, naive B cells and a few T  cells. The follicle centre cells within the germinal centres consist of cells with cleaved nuclei (centrocytes) and cells with larger  more open nuclei and several nucleoli(centroblasts). Stimulated mature B cells responding to antigen change into centrocytes and then centroblasts. The centroblasts leave the  follicle and pass to the paracortex and medullary sinuses, where they become immunoblasts. The immunoblasts divide to  give rise to plasma cells or memory B cells which are ready for their next encounter with specific antigen. Accessory cells:  Lymphocytes alone are not to make an effective immune response. They are assisted by so-called  accessory cells. These may be grouped as follows: •sinus macrophages (highly phagocytic)  •tingible body macrophages (ingest cellular debris in germinal centres)  •marginal zone macrophages (found beneath the subcapsular sinus)  •follicular dendritic cells
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Lymph node, rabbit - H&E The subcapsular and cortical sinus system was hardly (if at all) visible in the slides I looked at. Identify the connective tissue capsule and
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